1. Field of the Invention
The present invention relates to the field of earth boring tools and more particularly to rotating bits incorporating diamond elements as the active cutters.
2. Description of the Prior Art
Diamond bearing rotating bits historically have incorporated industrial quality natural diamonds as the cutting elements. These elements are fully embedded or surface set with 2/3 of the diamond within the bit in order to retain the small diamonds on the bit face under the tremendous stresses to which they were subjected during drilling. The sizes of such diamonds typically range from one to eight per karat and smaller.
Subsequently when polycrystalline diamond was first synthesized the fine diamond grit which was obtained was fabricated into larger usable pieces by sintering the diamond in a cemented system. One such diamond material is made by General Electric Co. and sold under the trademark, STRATAPAX. However, these synthetic diamond tables are temperature sensitive and tend to disintegrate at the higher temperatures such as routinely experienced in the furnacing of infiltration matrix bits. Therefore such prior art bits are able to use STRATAPAX cutters only by brazing the diamond tables to tungsten carbide studs and then disposing the studs into the steel bodied or matrix body bit.
Partially in response to the disadvantages arising from the thermal instability of STRATAPAX type cutters, somewhat more thermally stable diamond materials were developed. These materials include leached polycrystalline synthetic diamond similar to the cemented cobalt product typified by STRATAPAX cutters with the exception that all or a substantial part of the cobalt and similar cementing constituents have been acid leached from the sintered diamond. One such leached diamond product is manufactured and sold by General Electric Co. under the trademark GEOSET.
However, such leached diamond material presently commercially available is typically much smaller than the prior art STRATAPAX tables and ranges in size from a maximum of one per karat to three per karat or smaller. Therefore leached diamond product is of the same order of magnitude of size as natural diamonds and new designs were and are continuing to be demanded whereby leached diamond cutters within this size range can be usefully employed and retained upon a rotating drill bit. The prior art experience with natural diamonds, which were generally of cubic or round geometry, provides little if any instruction on how the triangular prismatic leached synthetic product can be best utilized in cutting teeth and on a drill bit to achieve high cutting rates and cutting lifetimes.
Therefore, what is needed is a design whereby synthetic polycrystalline diamond elements on a rotating drill bit can be employed in a manner to maximize cutting efficiencies, performance and lifetimes.